Saving Winnie & MaiAs the level starts, switch to Roofus and burrow into the hole in front of you. Now watch the opening. As the boss begins, start to shoot Mai (Chang's wife) who is holding on to Winnifred's neck. Avoid the green dog breath that Winnie breathes out, as it drains HP dramatically. When Winnie starts to shake, Mai will drop to the ground, so start shooting her to slow her down. Watch out for her laser eyes though - They pack a nasty punch. Look around for a hole to burrow through as you avoid her. When you burrow through it, you will come to a smaller area with a pool of liquid in the middle.
Switch to Chang if you need to, or grab the Pet Yums around the pool. Grab a Freeze Gun either way and wait until Mai comes through the small gap. Move left and right to help avoid her powerful laser eyes, and when she is in the pool of liquid, shoot her with the Freeze Gun. Whilst she is frozen, attack her either with your close attack or another weapon. She will break out of the ice and shield herself for a split second. Wait until she moves slightly, and repeat this process. Continue doing this until she walks out of the pool, without stopping to fire anymore of her laser eyes at you.
A cutscene will show Winnie re-appearing outside. Switch to Chang if you haven't done so already, and walk out of the small gap. Be careful - Watch closely for where Winnie is, avoid her dog breath, and run outside behind her so she doesn't catch up to you. I'd recommend staying around where Roofus' Telepoint is, since you'll be needing to burrow again soon. Attack Mai on Winnie's neck again, and once again, she will eventually fall off, and you will have to find the the hole and dig through it, switching to Roofus if you haven't already done so. You'll be inside the tree again. No matter which burrow you go through, you will always come out in this area, so stay alert in case Mai has already found you.
Shoot Mai with the Freeze Gun again and repeat your previous actions when she's in the pool of liquid, and switch to Chang again when Winnie comes out. Winnie will now use her dog breath and Mai will use her laser eyes at the same time from her position on Winnie's neck. Continue to shoot Mai, avoiding the attacks they both send out. After a while, they will eventually fall to the floor, and you can continue to the final stretch of the adventure.